IAEA-SM-361/29P XA9950122

Stable isotope composition of fluid inclusions preserved in derived from and Bochnia Beds (Southern )

M. Dulinsld', Z. Aiexandrowict, K. RJiarisJd1, A. ChiwtrJ

i} Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy al. Mickiewicza 30, 30-059 Krakow, Poland 31 Institute of Nature Conservation, Polish Academy of Sciences BL Lubicz 46,31-512 Krakow, Poland 3> Faculty of Geology, Geophysics and Environmental Protection, Unjverity of Mining and Metallurgy al. Mickjervicza 307 30-059 Krakow, Poland

Halite deposits located in the southern Poland, near Krakow, are famous mostly due to medieval mioe located in Wieliczka. Contrary to most salt deposits in Europe forming large domes, the halite deposits near Krakow form distinct beds, extending from west to east on the area of ca. 10 km2, with several types of salt identified . The deposits were formed in Miocene, ca. 15 mln years ago.

Stable isotope composition of fluid inclusions trapped in the halite crystals originating from Wieliczka and Bochnia salt mines was investigated. Two distinct groups of samples were analysed: (0 samples derived from so-called "green salt" beds forming extensive horizontal structures, and (ii) large nionocrystals of halite collected in crystal caves which form a part of the tourist tract within the Wieliczka Salt Mine. The samples belonging to the first group were heated under vacuum to extract the fluid inclusions, according to the procedure developed in our laboratory and used previously to extract inclusions from speleothem samples [ 1 ]. The macro-inclusions present in some monocrystals of halite collected in crystal caves were removed for analysis without any thermal treatment. The concentration of bivalent cations (Ca2*, Mg2*) was measured in the bulk material and in fluid inclusions (only second group). The *H and I8O isotope composition of fluid inclusions extracted from halite samples is presented in Fig. 1. The data points form two distinct clusters in the 52H - 5I8O space, corresponding to two groups of samples being analysed.

The cluster representing "green salt" deposit is shifted to the right-hand side of the WMWL, towards more positive 82H and 51SO values, pointing to evaporative conditions during formation of this deposit. Although the evaporation trajectories for the sea water, schematically shown in Fig.l suggest that fluid inclusions might represent remnants of the original solution, this notion has to be excluded due to the fact that only halite is present in the deposit. Other ions are present only in trace amounts. The isotopic composition of fluid inclusions formed during precipitation of halite phase from the sea water would be characterised by positive 52H and 518O values. The position of the cluster on 82H - S18O diagram suggest that the "green salt" deposits might have been formed in a lagoon-type environment, from mixture of sea water and water of continental origin.

The data points representing monocrystals of halite collected in the crystal caves lie close to the WMWL and cover the range of 52H and S!*O values typical for glacial/interglacial infiltration waters,in the southern Poland (cf. Fig.1). This suggest a much younger (Quaternary) age of the analysed monocrystals. A small systematic shift to the right-hand side of the WMWL, observed for five out of six data points, may indicate presence of different populations of monocrystals formed at different time windows characterised by slightly

158 different d-excess values of the local meteoric water line, or, alternatively, might reflect partial evaporation of the solution from which the crystals were formed. The conditions and possible mechanisms of formation of these secondary halite crystals are now being investigated and will be published elsewhere.

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Fig.l. Stable isotope composition of fluid inclusions trapped in halite deposits located near Krakow, southern Poland Circles and squares represent fluid inclusions extracted from "green salt" deposit The error bars reflect possible uncertainty associated with the extraction procedure of fluid inclusions. The full dots represent macro-inclusions present in monocrystals of halite collected in crystal caves, located within the salt deposit. The oval contours with numbers (1, 2, 3) indicate approximate range of 52H and 818O values of glacial, holocene, and pre-Quaternary infiltration waters, respectively, found in the southern Poland [ 2 }. Curved trajectory represent hypothetical evolution of the isotopic composition of sea water during evaporation and successive deposition of different [ 3 ]. REFERENCES

[1] Rozanski K. and DuHnski M, 1987 Deuterium content of European paJaeowaters as inferred from isotopic composition of fluid inclusions trapped in carbonate cave deposits. In: Isotope Techniques in Water Resources Development, IAEA, Vienna: 565-578.

[2] Grabczak J. and Zuber A., 1983. Isotope composition of waters recharged in the Quaternary in Poland. Freiberger Forschungshefte C38S: 93-108.

[3] Knauth L.P. and Beeunas M.A., 1986. Isotope geochemistry of fluid inclusions in Permian halite with impBcatfons for the isotopic history of ocean water and the origin of saline formation waters. Geochim. Cosmochim. Acta 50: 419-433.

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